Novel partial deletions, frameshift and missense mutations of CSF1R in patents with CSF1R‐related leukoencephalopathy

Background and purpose Colony‐stimulating factor 1 receptor (CSF1R)‐related leukoencephalopathy is an adult‐onset leukoencephalopathy caused by mutations in CSF1R. The present study aimed to explore the broader genetic spectrum of CSF1R‐related leukoencephalopathy in association with clinical and imaging features. Methods Mutational analysis of CSF1R was performed for 100 consecutive patients with adult‐onset leukoencephalopathy. Sequence and copy number variation (CNV) analyses of CSF1R were performed. The genomic ranges of the deletions were determined by long‐read sequencing. Ligand‐dependent autophosphorylation of CSF1R was examined in cells expressing the CSF1R mutants identified in this study. Results CSF1R mutations were identified in 15 patients, accounting for 15% of the adult‐onset leukoencephalopathy cases. Seven novel and five previously reported CSF1R mutations were identified. The novel mutations, including three missense and one in‐frame 3 bp deletion, were located in the tyrosine kinase domain (TKD) of CSF1R. Functional assays revealed that none of the novel mutations in the TKD showed autophosphorylation of CSF1R. Two partial deletions of CSF1R were identified that resulted in lack of the C‐terminal region, including the distal TKD, in two patients. Various clinical features including cognitive impairment, psychiatric symptoms and gait disturbance were observed. Various degrees of the white matter lesions and corpus callosum abnormalities on magnetic resonance imaging and characteristic calcifications on computed tomography were observed as imaging features. Conclusions Our results highlight the importance of examining the CNV of CSF1R even when Sanger or exome sequencing reveals no CSF1R mutations. Genetic examination of sequences and CNV analyses of CSF1R are recommended for an accurate diagnosis of CSF1R‐related leukoencephalopathy. Mutational analysis of CSF1R was performed for 100 consecutive patients with adult‐onset leukoencephalopathy. CSF1R mutations were found in 15 patients, accounting for 15% of the adult‐onset leukoencephalopathy. Seven novel mutations including missense mutations (p.N783D, p.K820N and p.F849I), an in‐frame deletion (p.K883del), frameshift mutation (p.E403fs*37) and two partial deletions of CSF1 were identified.